This application focuses upon the role of oocytes in the development of heterogeneous patterns of gene expression by different types of granulosa cells after follicular antrum formation. The investigator hypothesizes that oocytes promote the development of the cumulus cell phenotype by both suppressing and inducing expression of cell-specific transcripts. The Specific aims are to test: 1) the hypothesis that mouse oocytes promote expression of IGF-1 mRNA in granulosa cells of preantral follicles and cumulus cells of preovulatory follicles; 2) the hypothesis that oocytes from preovulatory follicles, but not those from preantral follicles, promote the expression of cumulus cell-specific transcripts; 3) whether oocytes from preantral follicles and antral follicles have different effects on kit ligand (KL) mRNA expression by granulosa cells and whether these different effects depend upon whether the granulosa cells are from preantral or antral follicles; and 4) whether species-specific patterns of granulosa cell gene expression are determined by oocytes in vivo.